The present invention relates to a system and method for blending gases in mixtures suitable for a variety of applications, such as for flushing vacuum vessels in which produce is stored to preserve the produce and inhibit adverse effects on the produce due to exposure to either too much or too little oxygen.
In some current systems for preserving produce, the produce is placed inside a plastic storage bag, from which the air is evacuated, and a gaseous mixture (typically containing less oxygen than atmospheric air) is introduced. The produce can be better preserved in this manner, both to prevent oxidation due to a high-oxygen environment—atmospheric oxygen being at a level of about 21%—and to prevent damage caused by an anaerobic environment.
With such a system, the gaseous mixture can be premixed, such that an accurate blend with a desired proportion of oxygen is achieved. However, a disadvantage arises from the fact that the flexible produce bags collapse upon evacuation, resulting in stress on and damage to the produce.
In other systems presently in use, produce may be placed in a rigid vacuum vessel and a gaseous mixture of appropriate oxygen content is introduced into the vacuum vessel. This may be accomplished, for instance, by first at least partially evacuating the vacuum vessel, then mixing some inert gas such as nitrogen from a pressurized nitrogen source with atmospheric air by the use of adjustable valves leading to a mixing chamber, and finally allowing the mixture to flow into the vacuum vessel. One problem with such a system is that, as the gas pressure within the vacuum vessel approaches atmospheric pressure, the nitrogen-air ratio may vary from that needed to achieve the desired resultant oxygen content in the mixture that reaches the vacuum vessel.
A system is accordingly needed wherein produce may be preserved by a gaseous mixture having a desired oxygen content, without physical damage to the produce and allowing real-time mixture of the introduced gases in the desired ratios.